Conventionally disclosed techniques detect an abnormal region in a living body based on pixel value gradient information, i.e. a pixel value surface shape feature value, in an endoscopic image, or detect an abnormal region based on edge information, i.e. a contour feature value, in an endoscopic image. Japanese Patent Application No. 2007-244519 discloses techniques that an abnormal region is detected by evaluating the isotropy of the pixel value gradient, that is, whether or not the gradient is equal in all directions, or evaluating whether or not the edge shape is a circular arc of a predetermined size.